COLOR AND CONSTITUTION RELATIONSHIPS IN ORGANIC PIGMENTS .3. PHTHALOCYANINES

Phthalocyanines provide the most important classical organic pigments in the blue and green shade area and some derivatives are of interest as near infrared absorbers. The results of PPP molecular orbital calcu lations, after refinement by parameter optimisation, were found to pro vide good agreement with experimental lambda(max) values for a range o f metal-free phthalocyanines and their complexes. The nature of the el ectronic excitation processes are discussed in terms of the calculated changes in pi-electron charge density.